Re: mass vs. volume measurement

Old Man wrote:

<snip> 

Yes. The normal method of "calibration" consists of
parts replacement, but, first, they check for radioactive
contamination and refuse to touch such.  Used properly,
contamiation isn't a problem.  So why do they check ?

<snip>

No, I think the calibration is a dispense into a calibrated cuvette. At least that's how I would do it.

Lots of lab equipment requires periodic calibration- I have a friend who works at Keithley, and they go way beyond anything I would ever do (and rightfully so, given their business). It's interesting talking to her about it.



Old Man once used a vapor pressure osmometer on
plant tissue samples.  Calibration every two hours, and
if room temperature was changing, it wasn't used at all.
Others in the lab used it (required, against their better
judgment) to check stock solution concentration.  They
just couldn't understand the need for prior calibration
(five measurements) nor the need for repeats after
calibration.  Fortunately for science, they weren't given
a choice.

Yeah, I still don't really understand how osmometers work. Something about freezing point depression, but it seems kinda voodoo.

--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
.